Implementation of ThemeResolver that uses a cookie sent back to the user
in case of a custom setting, with a fallback to the default theme.
This is particularly useful for stateless applications without user sessions.

ORIGINAL_DEFAULT_THEME_NAME

THEME_REQUEST_ATTRIBUTE_NAME

Name of the request attribute that holds the theme name. Only used
for overriding a cookie value if the theme has been changed in the
course of the current request! Use RequestContext.getTheme() to
retrieve the current theme in controllers or views.